The invention relates to a planar product in which a plurality of fibrous plies are bonded to each other by a special adhesive, and to the use of the adhesive for producing ply bonding of the fibrous plies. The present invention relates more particularly to tissue products and non-woven products in which bonding the plurality of plies is produced by said adhesive.
Tissue-making counts as a method of paper making, due to its basic agreement in the methods of production (wetlaying). However, tissue-making, better, raw tissue productionxe2x80x94where involving the single-ply (intermediate) product produced on a special paper-making machine for the production of tissue or tissue paperxe2x80x94differs from paper-making by its extremely low basis weight, usually of less than 65, more preferably less than 45 g/m2 and its very much higher tensile energy absorption index. The tensile energy absorption index materializes from the tensile energy absorption by relating the tensile energy absorption index to the test specimen volume prior to testing (length, width, thickness of the specimen between clamps prior to tensile loading).
In addition paper and tissue paper differs generally as regards the module of elasticity characterizing the stress/strain response of these planar products as the material characteristic as a function of the production conditions, the raw materials and chemical additives employed.
The high tensile energy absorption index of a tissue paper results from the outer and/or inner crepe. The former is produced by compression of the web of tissue paper adhering to the drying cylinder by the effect of a crepe knife, the latter by the difference in speed between two fabrics in sequence or, for example, between a sheeting fabric and one or two fabrics.
It is from this high tensile energy absorption index (see DIN EN 12625-4 and DIN EN 12625-5) that the majority of the useful properties as usual for tissue and tissue products result. One example are tissue products for hygiene applications (hygiene products, more particularly hygiene paper products) which find application in a wealth of cleaning functions, e.g. in personal grooming and hygiene, in home, industry and institutional areas. They are used to absorb fluids, for decorative purposes, for packaging or even just as supporting material, as is common for example in medical practices or in hospitals. Hygiene paper products with their broad range of applications count today as products for everyday use.
Hygiene papers include mainly all types of dry-creped tissue products, but also including wet-creped papers.
xe2x80x9cTissue papersxe2x80x9d or better, raw tissue papers are generally described as the single-ply intermediate products coming from the paper-making machine of lightweight papers, i.e. papers having a low basis weight which as a rule are dry-creped on a yankee cylinder with the aid of a crepe knife, whereby the single-ply raw tissue may be built up of one or more layers.
xe2x80x9cTissue productsxe2x80x9d are single or multi-ply finished products produced from raw tissue tailored to final consumer requirements, i.e. tailored in accordance with a requirements profile differing in many respects.
Typical properties of tissue products are their good ability to absorb tensile stress, their draping facility, good textile-like flexibilityxe2x80x94properties often termed bulk softnessxe2x80x94high surface softness, high specific bulk coupled with a perceptible thickness, an as high as possible liquid absorbency and depending on the application a suitably good wet and dry strength whilst featuring an interesting visual finish of the outer product surface. It is due to these properties that tissue papers are worked into tissue products (tissue paper products) available to final consumers in a wealth of different types and tailored applications, for example as wipes, towels, household and especially kitchen towels, as sanitary products (e.g. toilet papers), paper handkerchiefs, cosmetic tissues (facials) or serviettes/napkins.
Where multi-ply tissue products are concerned, care must be taken that the individual plies are bonded to each other by adequate ply bonding, although the ply bonding should not have a negative effect on the softness and absorptivity. Producing ply bonding by mechanical embossing pressure is disclosed for example by GB-C-363699. However, the ply bonding produced thereby is not particularly strong. Apart from this the necessary high embossing pressure may result in embossing knobs in the finished product which are conspicuous and rough to touch.
This is why ply bonding by chemical methods, i.e. gluing has materialized. Making use of an adhesive in this respect also in combination with mechanical techniques (embossing methods) have found application in producing ply bonding. U.S. Pat. No. 3,673,060 and U.S. Pat. No. 5,173,351 teach, for example, applying an adhesive in the region of the embossing roll directly to the side of the paper web to be later located on the inside of the multi-ply product.
The adhesives employed for a chemically produced ply bonding typical contain components soluble or dispersible in water such as polyvinyl alcohol (see also U.S. Pat. No. 3,673,060), polyvinyl acetate, carboxymethyl cellulose, starch etc.
Conventional adhesives have the disadvantage, however, that they lose their adhesiveness when wet and the individual plies become detached from each other when the tissue paper is used wet. The technical problem involved in this respect is the subject matter of WO 97/11226. This publication teaches the addition of a water-soluble cationic polymer (glyoxalated polyacrylamide, polyethyleneimine and preferably polyamide epichlorohydrine resin) to an adhesive on the basis of conventional adhesive components (starch, polyvinyl alcohol) to enhance the bonding capacity of the adhesive when wet.
The technique described therein for improving the ply bonding in multi-ply paper, more particularly in tissue products, does not always result in satisfactory ply bonding when dry and/or wet.
Problems associated with ply bonding when dry and/or wet may also be encountered in other planar products having a plurality of fibrous plies (more particularly cellulose fibrous plies) such as non-woven or textile plies.
The object of the present invention is thus to provide novel planar products, more particularly tissue products and non-woven products including a plurality of fibrous plies which excel by their ply bonding when dry and/or wet.